Cain Department of Chemical Engineering SEMINAR

 

Biomimetic colloidal self-assembly: toward artificial muscles and structural color

Michael J. Solomon
University of Michigan
Ann Arbor

Assemblies of colloids – microscopic particles that undergo Brownian motion and interact through physicochemical forces – are common both in nature and in advanced materials.  In this talk, we explore the possibility that colloidal self-assembly might be useful for forming soft matter that can reconfigure its shape or structure.   Such reconfigurable colloidal assembly could be applied to perform functions such as sensing, actuation, and coloration.  Similar scope for reconfiguration is already apparent in certain organisms, such as cephalopods; the reconfiguration in this case is due to changes in the stacking of plate-like proteins.  Such anisotropic particles are now widely available due to advances in particle synthesis; this availability is rapidly expanding the types of structures that may be assembled artificially.  Here we investigate how two types of anisotropy – ellipsoidal shape and Janus interaction – yield unexpected structures when their functionalities are combined into a single particle.  The colloids – called Janus ellipsoids – are produced by stretching latex spheres into ellipsoids, followed by evaporative deposition of a layer of gold onto one-half of the particle.  In aqueous solution, addition of electrolyte controls the relative binding of the two Janus faces of the ellipsoids.  Equilibrium structures produced include clusters, one-dimensional chains, and crystals with unusual stacking.  Direct visualization with two-color confocal microscopy reveals the specificity of the binding between the Janus ellipsoids.  The mechanism of the self-assembly is understood by means of simulation.  We apply AC electric fields to reconfigure between different chain-like structures of the ellipsoids.

Friday, March 16, 2018
2:00pm

1240 Patrick Taylor Hall